GitLab

- Adds new string for next button in cellular_setup page
- Abstracts CellularSetupPageName from cellular_page.js to a
  cellular_types.js
- Creates new esim_flow_ui page

- current UI https://imgur.com/owFzj4Z, will have another cl to update
  css and add images.
- UI spec https://docs.google.com/presentation/d/1Mfk5ZMEmeHwSbadUbyRU0Si5k6XDIvw-j4u7TUaCIGY/edit#slide=id.g7dc3c1fe01_5_115

Bug: 1093185
Change-Id: I5a9a960de9b5c578b5e46b322c972e27d17c38d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2348291
Commit-Queue: Nnamdi Theodore Johnson-kanu <tjohnsonkanu@google.com>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Azeem Arshad <azeemarshad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801515}